1. Field of the Invention
This invention relates to a signal receiver and a method thereof, a transceiver, and a network system, and particularly to improved signal receiver and method thereof, transceiver, and network system, wherein a reception frequency may be easily changed to a desired frequency.
2. Description of the Related Art
A superregenerative detection mode has characteristics such that a signal can be detected comparatively in high-sensitivity by a simple circuit configuration. So, for example, this superregenerative detection mode is applied to a keyless entry system for locking or unlocking a lock of a door of an automobile by utilizing a radio wave or an infrared ray.
FIG. 25 shows a construction of a well-known superregenerative circuit utilized in such a keyless entry system. This superregenerative circuit includes an adder 1, an amplifier 2 for amplifying a signal from the adder 1 to produce an output, an extraction circuit 3 for extracting a part of the output from the amplifier 2 to be fed back to the adder 1, and a quenching oscillator circuit 4 for controlling an amplified degree of the amplifier 2, in which the adder 1 adds a signal extracted by the extraction circuit 3 to a received signal of a radio wave transmitted from a signal transmission apparatus through an antenna (neither is illustrated).
The signal, which was transmitted from the signal transmission apparatus and received by the antenna, is entered into the amplifier 2 through the adder 1. The amplifier 2 amplifies the input signal and produces an amplified output. The amplification degree of the amplifier 2 is controlled for the correspondence to the signal which the quenching oscillator circuit 4 outputs. An oscillation frequency of the quenching oscillator circuit 4 is set by a predetermined frequency much lower than a carrier frequency of the transmitted signal entered into the adder from the signal transmission apparatus.
The extraction circuit 3 extracts a frequency component of the carrier of the received signal from output of the amplifier 2 to be applied to the adder 1. The adder adds the signal supplied by the extraction circuit 3 to the received feeble signal to be applied to the amplifier 2. When the level of the entered modulation signal is almost zero, the high frequency oscillation action of the superregenerative circuit does not stop, but the entered modulation signal is in a weak oscillation state. The oscillation becomes strong by addition of the signal of the carrier frequency to produce the signal from the amplifier 2. The superregenerative circuit synchronizes with the carrier frequency to make a high frequency oscillation allowing the output of the amplifier 2 to become a signal of a carrier at a large level.
Thus, the carrier at a large level is produced from the amplifier 2 when a modulation signal exists, whereby the signal transmitted from the signal transmission apparatus may be read by detecting the carrier.
In this way, superregeneration is executed in the superregenerative circuit by employing the extraction circuit 3 in the feedback route and feeding back a component of a predetermined frequency from the extraction circuit 3. Accordingly, the extraction circuit 3 is composed of an LC resonance circuit or a delay line of SAW (Surface Acoustic Wave). When the reception frequency is required to be changed, however, for example, a value of the coil or the capacitor in the LC resonance circuit has to be adjusted into a different value by a manual operation. As schematically shown in FIG. 26, there is the problem that the frequency bandwidth for superregeneration can be adjusted only to a small extent. If the delay line of SAW represents the extraction circuit 3, there is a problem such that the frequency may not be changed.
It is, therefore, a primary object of this invention to provide a superregenerative circuit where the reception frequency may be adjusted among a wide range of values.
According to an aspect of this invention, there is provided a signal receiver including a superregeneration means for feeding back a part of an output signal to form part of an input signal through a feedback route to execute a superregeneration, a capacitance element disposed in the feedback route of the superregeneration means, a switching means for switching the capacitance element, and a generating means for generating a clock signal for switching the switching means based on an output of the superregeneration means.
According to another aspect of this invention, there is provided a transceiver including a signal transmitter for transmitting a signal to other transceiver, and the above-mentioned signal receiver for receiving a signal transmitted from the other transceiver.
According to a further aspect of this invention, there is provided a network system including a plurality of the above-mentioned transceivers.
According to still another aspect of this invention, there is provided a signal reception method including the steps of generating a clock signal for switching a switching means based on an output of the superregeneration means, and of switching the switching means based on the generated clock signal.
In the above-mentioned signal receiver and the signal reception method, the switching means is designed to switch the capacitance element for the correspondence to the clock formed based on the output of the superregeneration means, whereby the superregenerated frequency may be adjusted to an optional value.
The above-mentioned transceiver and the network system employ the above-mentioned signal receiver, whereby the frequency may be adjusted to an optional value for signal receipt and transmission.